1. Field of the Invention
The present invention relates to an oil seal for a door closing device that has a longer longevity.
2. Description of the Related Art
Taiwan Utility Model Publication No. 342025, issued on Oct. 1, 1998 and entitled xe2x80x9cBASE STRUCTURE FOR A DUAL-FUNCTION DOOR CLOSING DEVICExe2x80x9d, as illustrated in FIGS. 1 and 2 of the drawings, discloses an automatic door closing device 9 that is mounted to a door. When the door is opened, a shaft 91 is turned, a movable plug 93, via transmission by a gear 92 on the shaft 91 and a rack (not labeled) that is formed on the movable plug 93 and meshed with the gear 92, is moved to compress an elastic element 94 and make working fluid to flow. When the force that opens the door vanishes, the door is automatically closed under the action of the return force of the elastic element 94 and back flow of the working fluid. An oil seal 95 is mounted to the shaft 91 to avoid leakage of the working fluid via a gap between the cover 96 and the shaft 91. Nevertheless, during flow, the working fluid exerts a force on the oil seal 95 and thus makes the oil seat 95 press against a peripheral edge 97 defining a central annular hole of the cover 96. After a term of usage, the oil seal 95 deforms. Or, an annular recess is generated due to friction between the oil seal 95 and the peripheral edge 97 of the cover 96. Leakage occurs accordingly, as the oil seal 95 no longer provides the required sealing effect.
It is an object of the present invention to provide a door closing device with an oil seal that is not easy to deform and damage and is thus durable.
A door closing device in accordance with the present invention comprises a main body, a shaft, an annular cover mounted in the main body, and a planar gasket. Two ends of the shaft are rotatably supported in the annular cover by a collar. The planar gasket is mounted around the shaft and between the collar and a peripheral edge defining a central annular hole of the annular cover. The planar gasket includes an inner diameter approximately the same as an outer diameter of the shaft and an outer diameter approximately the same as an inner diameter of the annular cover. The planar gasket further includes two opposed planar surfaces.
The planar gasket is made from an oil-resisting material, such as tetrafluoro-ethane resin.
Other objects, specific advantages, and novel features of the invention will become more apparent from the following detailed description and preferable embodiments when taken in conjunction with the accompanying drawings.